Scroll compressors typically include two interfitting scroll members, each having a base and a generally spiral wrap extending from the base. The two wraps interfit to define a pair of compression chambers in which refrigerant is compressed in a parallel manner.
Refrigerant ideally enters the chambers in equal amounts, and the chambers then seal and move toward a compressor discharge. Additional refrigerant can be added to the compression chambers by various options, such as the injection of an economizer fluid or liquid injection.
An economizer fluid is returned to the compressor when an economizer cycle is in operation. Essentially, an economizer cycle taps a flow of refrigerant downstream of a heat exchanger which receives a compressed refrigerant from a compressor. The tapped refrigerant is expanded, and passed through an economizer heat exchanger where it cools a main refrigerant flow. This increases the cooling capacity of the main refrigerant flow. The tapped fluid, having passed through the economizer heat exchanger, is returned to the compressor. Typically, the returned fluid is injected into the compression chambers at an intermediate point in the compression cycle.
Efforts are made to ensure that the pressure of refrigerant to be compressed in each of the opposed compression chambers is equal. However, in practice, it has been difficult to ensure that the pressure is equal. It becomes particularly difficult to ensure equal pressure when the economizer function is in operation and vapor is being injected into the compression chambers. It is also difficult to assure that pressure remains equal within the compression chambers when liquid injection is used to reduce the compressor discharge temperature.
Different pressure in the two intermediate compression chambers leads to additional losses during porting, as the refrigerant streams of different pressure will merge into a common discharge chamber as the refrigerant exits form each of the intermediate compression chambers. This results in additional mixing losses as two streams of different pressure merge together during porting. Having different pressure at each compression chamber during porting also makes it impossible to achieve an optimum built-in volume ratio for a rating point, because at least one parallel compression path during compression will operate at the non-optimum built-in pressure ratio.
Historically, scroll compressors had wraps which were of a generally constant thickness. However, with further design development, much study went into the shape of the wraps. The wraps are now often of a varying shape for many different design reasons. These varying shapes have varying thicknesses. Such varying thickness shaped wraps are known as “hybrid” wraps. The problem mentioned above becomes especially acute for a hybrid-type scroll wrap profile, as the injection ports for the economizer fluid have different geometry and sizes for each compression chamber. Having different geometry ports makes it especially difficult to achieve equal pressure in each compression chamber, because depending on the operating condition it would be difficult to inject the same amount of refrigerant into each chamber.
It is known in the prior art to have a groove, which connects the two opposed compression chambers in an attempt to equalize pressure between the chambers. An example is illustrated in U.S. Pat. No. 6,171,086. However, this prior art method only communicates the two chambers for a short period of time.